A mouthrinse containing chitosan or pharmaceutically acceptable acid addition salt thereof with fluoride ions, for use against erosive tooth demineralization, and kits containing chitosan or pharmaceutically acceptable acid addition salt thereof with fluoride ions, wherein one of the two active agents is comprised in a mouthrinse, are described. The mouthrinse may furthermore comprise dissolved tin, in particular stannous ions. Mouthrinses containing chitosan or pharmaceutically acceptable acid addition salt thereof with fluoride ions are tested in the treatment or prevention of erosive tooth demineralization caused by citric acid.
